This is a free preview of a paid episode. To hear more, visit mskmag.substack.com

The cells of a malignant tumour are restless. Every so often, one wriggles free and breaks off. It’s almost certainly doomed: if it’s not destroyed by immune cells, it will likely succumb to fluid shear stress as it’s dragged through narrow vessels, or just undergo programmed cell death [1].

But some do make it to the spine and colonise it; we then call them metastases. Why so often the spine and not, say, the tibia or the deltoid?

People often blame Batson’s plexus: blood draining back to the heart can be accidentally shunted into the venous plexus of the spine - Batson's plexus - because it lacks valves [2]. Those itinerant cancer cells can ride the shunt and make a home in the spine.

That’s part of it, but the bigger reason is that the spine has something cancer cells want [3]. Stephen Paget suggested this first in 1889 [4], and he’s been proven mostly right [1]: “some bones suffer more than others; the disease has its seats of election... When a plant goes to seed its seeds are carried in all directions; but they can only live and grow if they fall on congenial soil.”